Metallic interconnects can suffer from failure due to electromigration (EM) when exposed to high current densities. EM occurs primarily along interfaces such as grain boundaries or phase boundaries and to a lesser degree in the bulk (grain). Attempts at improving EM resistance have included using metal alloys with precipitates at the interfaces, capping the interconnect with a rigid material to resist EM surface diffusion, and using alloys and deposition techniques that can deposit large contiguous grains referred to as “bamboo grains.”
These existing approaches, however, are based on using the as-deposited microstructure with little change beyond typical thermal annealing from sources external to the chip (for example, an oven or a laser).
Thermal anneals, often with excursions to much higher temperatures, are also used in other aspects of silicon technology such as a modification of dopant profiles, a relaxation or build up of stress, or an increase in the adhesion between layers. These material properties are typically improved through a difficult engineering of the thermal history that allows for the nanometric controlling of diffusion in materials. Thermal anneals are also needed to engineer contacts.
As scaling of devices continues, the contact area is becoming sufficiently small that the intrinsic contact resistivity of the Si/Silicide interface can dominate the external resistance of a device. By way of example, at a typical contact resistivity value of 10−8 Ω-cm2, a contact length of 10 nm represents 100 Ω-μm per interface, which represents more than the entire external resistance budget for a device. Reducing the intrinsic contact resistivity to improve the device performance could be accomplished, for instance, by annealing the interface and allowing for selected impurities to diffuse to the interface. A relatively high thermal budget might be required to achieve such a low interfacial resistivity.
However, other elements of the devices or integrated circuits may not be in a position to withstand such an anneal. In this particular application, there is a need for anneal techniques that deliver heat locally to the element that can benefit from it without damaging other components that are sensitive to the thermal budget.